Cooking with Linux - Lights...Camera...Action!

Set up a simple video studio with only a Webcam, microphone and these open-source packages.

I'm afraid it's true, François. The camera does not lie. That's what you
look like when you are serving wine. Of course, mon
ami, I have no
intention of putting this little video on our restaurant's Web site. Why
am I doing this? Ah, you have not yet looked at the feature for today's
menu. Multimedia and entertainment is the ticket, mon
ami, and
you have to admit, this little video certainly is entertaining. Don't be
upset, François, I have the ultimate respect for you. Besides, there's
no time to fret, our guests will be here any moment. Ah, you see, they
are already at the door.

Welcome, mes amis, to Chez
Marcel! It's wonderful to see you all
today here at the finest Linux restaurant on the planet, which also happens
to be the home of one of the greatest wine cellars in the world. Please
sit and make yourselves comfortable. François was just heading to the
wine cellar now. The 2001 Santa Lucia Highlands Pinot Noir is drinking
very nicely. It's a showy wine, bursting with hints of stardom—perfect for today's menu.

As you will notice, each workstation today is equipped with a small
Webcam and microphone. The immediate idea is that we
(or someone else) will wind up as the star of our little movie, but
sometimes the software itself is the star. After all, many an application
has shone on Chez Marcel's menu, non?
And, this is where Karl Beckers' xvidcap
comes into play. xvidcap is a great little tool for recording the action
on your X desktop using a program called ffmpeg, which
likely is already on your system.
The
result is an MPEG movie of your entire desktop or any portion thereof.

Why would you do such a thing, you might ask? Well, you can use this to
create a training video to show others how to use an application or to
show the world how good you are at playing your favorite first-person
shooter. To get your copy of xvidcap, head on over to the official
Web site (see the on-line Resources).
The site offers both source and some binary packages, such as RPM or
DEB. Should your particular distribution not be covered, building xvidcap
from source is a simple extract and build five-step:

The program name is either xvidcap or gvidcap. I say
either because if you have the GTK2+ development libraries (version
2.2.1 or later), you get a second binary. Both work the same but,
quite honestly, the GTK2+ interface looks and works better. If you don't
have a recent GTK2+, you still may be able to get the interface by using
one of the binary packages as opposed to source.

When you start either version of the program from the command line, you
see a simple toolbar with a few buttons and a red rectangle floating
below it. This is the capture window, and you can move it to cover whatever
area you want to record. The default window, however, is fairly small. To
change the area you want to record, click the crosshairs icon (second
from the right on the toolbar), then click and drag the pointer to take
in whatever area you want to include in your capture. The red rectangle
will be resized. The toolbar contains buttons to record, stop, pause and so on. Pausing
over the buttons will display tool tips. That's it, you are recording
a movie of whatever transpires inside the red rectangle (Figure 1).

Figure 1. Selecting
a Capture Window with xvidcap/gvidcap

Some preference settings let you change the
number of frames per second, the video codec
and whether you want to capture the mouse pointer in the
final video. Right-click on the frame button (first on the left) and
select Preferences (Figure 2). After you've experimented for a while,
type man xvidcap for details on running the program without
the GUI. The added bonus is that you can capture audio as well, which is perfect
if you are creating an instructional video.

Figure 2. The gvidcap
Preferences Dialog

One of the reasons I made a point of mentioning ffmpeg when
introducing xvidcap is that it is an amazingly versatile little program
and well worth getting to know. You can use ffmpeg to create your own
movies with next to no expense. A cheap Webcam and, assuming you want
sound, an equally cheap microphone are all you need (and ffmpeg,
of course).

A few weeks ago, I was asked to create an introductory video for a
book project. The quality wasn't expected to be exciting, because this was
mostly a proof-of-concept thing and not meant to be the final product.
Because I did not have a proper video
camera, I had to improvise and thereby created what might well be the
world's cheapest video recording studio (Figure 3). My setup was a cheap
microphone and a cheap USB Webcam with a CPIA chip. Armed with
my Linux system, I figured I was ready to go. The only question was
“How?”

Figure 3. Is this the
world's cheapest video recording studio?

Using ffmpeg, I created my video clip, experimented with timing,
frame rate and so on, until I had something that was getting pretty
good. With the following command, I created an AVI format video clip at
ten frames per second:

That's it. My video device input (indicated by the -vd
option) is /dev/video and my sound, or audio, input was
/dev/sound/dsp. That's the -ad option. Your own devices
may be a little different of course. For instance, on another of my
machines, the USB video device is /dev/video0. As it stands,
the command continues to record until you
run out of disk space. So, to limit a recording to ten seconds, I use the
-t option:

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